In the related art, it has been attempted to mitigate traffic jams by improving the traffic volume on a load through controlling the travelling of individual vehicles. For example, Patent Literature 1 discloses a preceding vehicle follow-up device that detects changes in the inclination on the forward side of a traveled road, and in a case where the change in the inclination is detected in the vicinity of a sag (a point of change from downhill to uphill on the road) or the like on the forward side of the traveled road, switches from inter-vehicle distance control to vehicle speed control. The preceding vehicle follow-up device disclosed in Patent Literature 1, in the vicinity of a sag, is switched from inter-vehicle distance control to vehicle speed control to suppress a variation in vehicle speed during the preceding vehicle follow-up control. Particularly, in the preceding vehicle follow-up device described in Patent Literature 1, even when the inclination changes on a sag when a plurality of vehicles are traveling in a sequence, the preceding vehicle follow-up device prevents the variation in the vehicle speed of a preceding vehicle from being amplified and propagated to the following vehicles.